As a nonvolatile semiconductor storage device capable of electrically performing writing and erasing operations, an EEPROM (Electrically Erasable and Programmable Read Only Memory) has been widely used. Such a storage device has a trapping insulating film or a conductive floating gate electrode surrounded by an oxide film below a gate electrode of an MISFET, and reads, as a threshold of a transistor, storage information that is a charge storage state in the floating gate or the trapping insulating film (charge retention part).
The trapping insulating film means an insulating film capable of storing a charge, and, for example, a silicon nitride film or others is cited as one example. By injecting and discharging the charge to and from a charge storage region, the threshold of the MISFET is shifted so as to be operated as a storage element. As the nonvolatile semiconductor storage device using the trapping insulating film, a split gate-type cell using an MONOS (Metal Oxide Nitride Oxide Semiconductor) film is cited.
Patent Document 1 (Japanese Patent Application Laid-open Publication No. 2014-72484), Patent Document 2 (Japanese Patent Application Laid-open Publication No. 2005-123518), Patent Document 3 (Japanese Patent Application Laid-open Publication No. 2012-94790) and Patent Document 4 (Japanese Patent Application Laid-open Publication No. 2004-111749) describe that a taper is formed on a side surface of a control (selection) gate electrode in the split gate-type MONOS memory. Moreover, Patent Document 3 describes that a lower portion of a side surface of a control gate electrode adjacent to a memory gate electrode is recessed through ONO (Oxide Nitride Oxide).